How hard is middle English to learn? How much am I going to have to work to be able to read Chaucer in the original language?
Chaucer is relatively easy. His writing is more direct and easy to follow than Shakespeare despite all the weird-ass spellings. If you've got annotations to explain the various archaisms that pop up, you should be good. The prologue is probably the hardest part but after a while you get used to the Middle English.
It's just the matter of annoyingly working out the phonetics til you get the word. It's not worth it at all, a conversion into modern spelling would render it literally identical minus all the annoyance.
I think you'd prefer the sound of Middle English, even if it's harder, it qualifies as music.
you can start reading chaucer right now.
in general, it and even old english are easier for a native english speaker to learn than any foreign language. the big issue is the complete lack of modern material, which means you'd need to be borderline autistic to immerse yourself to the extent required to reach 'fluency' (in so far as such a concept is possible with an extinct language/dialect).